We tested the effects of Verapamil and Nifedipine on intramyocardial pH during myocardial ischemia to determine whether Verapamil and Nifedipine improve myocardial acidosis following coronary occulusion in dogs. Verapamil, but not Nifedipine, improved acidosis of ischemic myocardium. there was no difference among groups treated with Verapamil, Nifedipine or placebo in ischemic zone myocardial blood flow or mean aortic pressure. Verapamil, but not Nifedipine, lowered heart rate. However, analysis of covariance showed higher ischemic zone pH for any heart rate during Verapamil compared to Nifedipine or placebo, indicating direct effect of Verapamil indenpendent of heart rate. Thus, the mechanism of improved ischemic zone pH by Verapamil probably involves a direct effect on ischemic myocardium, e.g., decreased ischemic zone contractile function.